Time division multiple access (TDMA) systems, such as GSM, have a plurality of time slots in a given time frame. For example in GSM each TDMA time frame has eight time slots. Conventionally, each time slot is reserved for use by a particular user.
Digital mobile communication systems for voice such as GSM (Global System for Mobile Communication), and DAMPS (Digital Advanced Mobile Systems) have expanded very rapidly in recent years.
In addition great demand for data service has been created by mobile users due to wide spread acceptance of the Internet. GPRS (General Packet Radio Service), EDGE (enhanced data rate for GSM), and UMTS (Universal Mobile Telecommunications Services) are all being developed to accommodate data users in wireless networks.
Schemes for the transmission of voice over fixed packet switch networks have also been developed in recent years and an increasing amount of voice traffic will be carried over packet switched networks in the future.
The enhanced data rate for GSM evolution (EDGE) is a proposal for the evolution of existing time division multiple access (TDMA) radio cellular systems in order to support higher transmission data rates and increase the capacity of these networks. The application of EDGE is restricted not only to GSM cellular networks but also has been accepted for the evolution of IS-136 systems by UWCC (Universal Wireless Communications Consortium). Enhanced data rates are achieved by introducing higher level modulation formats, such as 8-PSK (phase shift keying). With the introduction of such modulation schemes, EDGE systems can offer bit rates of up to approximately three times higher than standard GSM/GPRS/IS-136 systems.
EDGE was initially developed in order to provide data service at higher rates than GSM or GPRS, by making use of multi-phase modulation (such as 8-PSK) instead of binary GMSK. However, the structure of the proposed RLC/MAC blocks for data transmission do not allow for the efficient use of the available radio resources for voice transmission. Furthermore, due to the use of 8-PSK more powerful channel coding is required in order to maintain certain levels of voice quality.
It is an object of the present invention to provide an efficient transmission scheme for interleaving data from different users in the time slots of a TDMA frame, which is particularly suited to the transmission of voice in an EDGE network.